The present invention generally relates to an apparatus comprising a xe2x80x9cprinter head for electronic printingxe2x80x9d of the type which is shown and described in the Swedish patent Nr 9903000-9 (PCT/SE00/01622) having validity from Aug. 25, 1999, and which, in turn, is built on a method for printing on paper by means of toner and based on U.S. Pat. No. 3,689,935 (Pressman/Casanova).
By having toner, in the form of a dry ink powder, flow through several narrow bores of a bore matrix, which is arranged so that it is possible to open and close, alternatively, selected bores of said bore matrix. The toner powder is adapted to create meaningful signs. The bores of the bore matrix is controlled both by means of an electric field which is applied over the bore, which field closes and opens, respectively, each separate bore, and also by means of an electric main field that transports toner down from the bore to a paper located underneath the matrix when the bore is open. In order to have toner react on said two different electric fields, which are created round the bore, the toner particles must be electrically charged. The toner, which is normally available on the market, is formed so that it can be charged to a negative electric charge. Said charging is provided in that the toner particles are rubbed mechanically against a material having such properties as to charge the toner to a negative potential.
The above mentioned Swedish patent (=PCT application) describes a method for creating a main field from a metal layer, which is located on the upper surface of the bore in the bore matrix, and down to a pulling electrode which is mounted underneath the matrix bore. The paper is positioned between the pulling electrode and the matrix bore, and the toner will deposit on said paper after having passed the bore. At the lower surface of the bore matrix there is an electrically conducting ring round each bore, which ring is connected to a relay circuit which can apply an electric potential round each separate bore. Thereby there is formed a field from the upper surface of the bore to the lower surface thereof, which field can have the same direction as that of the main field, whereby the bore is xe2x80x9copenxe2x80x9d for passage of toner. If the field is applied in a direction which is opposite to the main field the bore will be xe2x80x9cclosedxe2x80x9d for passage of toner.
The patent also discloses a method of creating a cloud of charged toner particles above the matrix bore, which cloud is floating (air suspended) and is in continuous movement in that toner is thrown out from a brush down towards the bore. The toner which is not used will either mechanically rebounce into the brush or will be pulled into the brush in case said brush has a positive electric potential.
In the priorly known technical art the toner particles are transported from a toner container by means of a feeder brush down to a printer brush, where the toner is released using a rip off bar to form a cloud of toner particles which find their way to open bores of the bore matrix but which may also deposit on the upper surface of the bore matrix where they provide dots of non used toner particles which have to be removed in some way. If said toner is not removed the space between the brush and the bore matrix will be filled with toner and the entire printing process will cease. It may also happen that some toner particles, for various reasons, become charged to the wrong potential. Such wrongly charged toner particles may cause problems in that the bore matrix becomes dirtied at the bottom surface of the toner matrix and that the printed paper becomes dirty. It may be difficult to remove such wrongly charged toner particles.
The present invention is intended to solve the problems in the priorly known technical art and to suggest an alternative of how to transport toner from a toner container using a feeder brush down to a printer brush and further down through the bore matrix and as far as to the paper to be printed. According to the invention the toner particles are charged by being mechanically rubbed against the printer brush using charging ridges. The apparatus also includes means for removing toner particles which, for various reasons, have become wrongly charged by the printer brush, and means for forming a cloud of free toner particles which move inside the brush between the brush fibers, and whereby said brush finally keeps the metal layer above the bores of the bore matrix free from toner.